1. Field of the Invention
This invention is in the field of medicinal chemistry. In particular, the invention relates to carbocyclic and heterocyclic substituted semicarbazones and thiosemicarbazones, and the discovery that these compounds act as blockers of sodium (Na+) channels.
2. Related Art
Several classes of therapeutically useful drugs, including local anesthetics such as lidocaine and bupivacaine, antiarrhythmics such as propafenone and amioclarone, and anticonvulsants such as lamotrigine, phenytoin and carbamazepine, have been shown to share a common mechanism of action by blocking or modulating Na+ channel activity (Catterall, W. A., Trends Pharmacol. Sci. 8:57-65 (1987)). Each of these agents is believed to act by interfering with the rapid influx of Na+ ions.
Recently, other Na+ channel blockers such as BW619C89 and lifarizine have been shown to be neuroprotective in animal models of global and focal ischemia and are presently in clinical trials (Graham et al., J. Pharmacol. Exp. Ther. 269:854-859 (1994); Brown et al., British J. Pharmacol. 115:1425-1432 (1995); SCRIP 1870:8 (1993); SCRIP 1773:14 (1992)).
The neuroprotective activity of Na+ channel blockers is due to their effectiveness in decreasing extracellular glutamate concentration during ischemia by inhibiting the release of this excitotoxic amino acid neurotransmitter. Studies have shown that unlike glutamate receptor antagonists, Na+ channel blockers prevent hypoxic damage to mammalian white matter (Stys et al., J. Neurosci. 12:430-439 (1992)). Thus, they may offer advantages for treating certain types of strokes or neuronal trauma where damage to white matter tracts is prominent. In addition to playing a major role in neurotoxicity involving stroke, glutamate is also a key neurotransmitter which mediates otoneurotoxicity resulting in acute or progressive hearing loss and tinnitus (Pujol et al. Acta Otolaryngol (stockh) 113:330-334 (1993). Therefore, Na+ channel blockers are expected to be effective in preventing and treating otoneurotoxicity by decreasing extracellular gluatmate concentration. Similarly, Na+ channel blockers will be useful for preventing and treating eye diseases involving excitatory toxicity such as glaucoma and CMV retinitis.
Another example of clinical use of a Na+ channel blocker is riluzole. This drug has been shown to prolong survival in a subset of patients with ALS (Bensimm et al., New Engl. J. Med. 330:585-591 (1994)) and has subsequently been approved by the FDA for the treatment of ALS. In addition to the above-mentioned clinical uses, carbamazepine, lidocaine and phenytoin are occasionally used to treat neuropathic pain, such as from trigeminal neurologia, diabetic neuropathy and other forms of nerve damage (Taylor and Meldrum, Trends Pharmacol. Sci. 16:309-316 (1995)), and carbamazepine and lamotrigine have been used for the treatment of manic depression (Denicott et al., J. Clin. Psychiatry 55: 70-76 (1994)).
It has been established that there are at least five to six sites on the voltage-sensitive Na+ channels which bind neurotoxins specifically (Catterall, W. A., Science 242:50-61 (1988)). Studies have further revealed that therapeutic antiarrhythmics, anticonvulsants and local anesthetics whose actions are mediated by Na+ channels, exert their action by interacting with the intracellular side of the Na+ channel and allosterically inhibiting interaction with neurotoxin receptor site 2 (Catterall, W. A., Ann. Rev. Pharmacol. Toxicol. 10:15-43 (1980)).
PCT International Published Application WO94/06758 discloses a genus of aryl semicarbazones that have anticonvulsant activity in the maximal electroshock screen when orally administered to rats.
Dimmock et al., J. Med. Chem. 36:2243-2252 (1993) discloses aryl semicarbazones and aryl thiosemicarbazones that display oral activity as anticonvulsants in rats.
PCT International Published Application WO96/40628 discloses semicarbazones represented by Formula IX: 
where R1-R4 are independently hydrogen, halogen, C1-9 alkyl, C3-9 cycloalkyl, cyano, C1-9 alkoxy, or C6-10 aryloxy; R5 is hydrogen, C1-9 alkyl, C3-9 cycloalkyl, or C6-10 aryl; and X is oxygen or sulfur. The compounds are disclosed to be useful as anticonvulsants.
Dimmock et al., J. Med. Chem. 39:3984-3997 (1996) discloses (aryloxy)aryl semicarbazones that displayed anticonvulsant activities when administered intraperitoneally to mice or orally to rats.
The compounds that are disclosed in each of the aforementioned documents are described as having anticonvulsant activities. However, their mechanism of action had not been elucidated.
The present invention is related to treating a disorder responsive to the blockade of sodium channels in a mammal suffering from excess activity of said channels by administering an effective amount of a compound of Formula I or Formula IX as described herein. The present invention is also related to treating a disorder responsive to the blockade of sodium channels in a mammal suffering therefrom by administering an effective amount of a compound of Formula VI as described herein.
The present invention is also directed to the use of a compound of Formulae I, VI or IX for the treatment of neuronal damage following global and focal ischemia, for the treatment or prevention of otoneurotoxicity, for the treatment and prevention of eye diseases involving excitatory toxicity, and for the treatment or prevention of neurodegenerative conditions such as amyotrophic lateral sclerosis (ALS), as antimanic depressants, as local anesthetics, as antiarrhythmics and for the treatment or prevention of diabetic neuropathy and for the treatment of pain including chronic pain. The compounds may also be useful for urinary incontinence.
The present invention also is directed to the process for preparing novel substituted semicarbazones and thiosemicarbazones of Formulae I or IX.
A first aspect of the present invention is directed to the use of compounds of Formulae I, VI or IX as blockers of sodium channels.
A second aspect of the present invention is to provide a method for treating, preventing or ameliorating neuronal loss following global and focal ischemia; treating, preventing or ameliorating pain including chronic pain; treating, preventing or ameliorating neurodegenerative conditions, otoneurotoxicity and eye diseases involving glutamate toxicity; treating, preventing or ameliorating manic depression; inducing local anesthesia; and treating arrhythmias by administering a compound of Formulae I, VI or IX to a mammal in need of such treatment.
A number of compounds within the scope of the present invention are novel compounds. Therefore, a third aspect of the present invention is to provide novel compounds of Formulae I or IX, and to also provide for the use of these novel compounds for treating, preventing or ameliorating convulsions.
A fourth aspect of the present invention is to provide a pharmaceutical composition useful for treating disorders responsive to the blockade of sodium ion channels, containing an effective amount of a compound of Formulae I, VI or IX in admixture with one or more pharmaceutically acceptable carriers or diluents.
A fifth aspect of the present invention is directed to methods for preparing novel compounds of Formulae I or IX.